The run-out characteristics of a rotor supported by an externally pressurized gas-lubricated journal bearing are investigated in this research with a special attention to the relation with the machining errors of the rotor and the bearing. The obtained results are summarized as follows :(1) The modified divergence formulation method to analyze the pressure distribution in the bearing clearance is established with taking into consideration the effect of divergent flow from discrete supply holes. The fundamental characteristics of the bearing with machining errors are studied by applying this method.(2) A theoretical model to account for the run-out of a rotor supported by an externally pressurized gas-lubricated journal bearing is proposed in which the machining errors such as out-of-roundness of the journal and size deviation of supply holes are attributed to cause the rotor run-out. Static and dynamic run-out characteristics are discussed on the basis of the calculated results.(3) A design criterion for maximum bearing stiffness, which is currently applied at the bearing design, is compatible with precision design criterion with respect to the rotor run-out.(4) The rotor run-out is determined mainly by out-of-roundness of the rotor, but is scarcely affected by the size deviation of the supply holes.(5) The run-out characteristics of the rotor are substantially related with the combination of the number of lobes of rotor cross-section, m, and the number of supply holes, k. The most critical situation for rotor run-out is such a case with m=k+1.以上の成果をもとに,本研究で確立した手法により,回転精度からみた気体軸受の精度設計のための理論的背景を与えることができると考える。